Chloride is an electrolyte, a negatively charged molecule that works with other electrolytes, such as potassium, sodium, and bicarbonate (sometimes measured as total carbon dioxide [CO2]), to help regulate the amount of fluid in the body and maintain the acid-base balance. Chloride is present in all body fluids but is found in the highest concentration in the blood and in the fluid outside of the body’s cells. Most of the time, chloride concentrations mirror those of sodium, increasing and decreasing for the same reasons and in direct relationship to sodium. When there is an acid-base imbalance, however, blood chloride levels can change independently of sodium levels as chloride acts as a buffer. It helps to maintain electrical neutrality at the cellular level by moving into or out of the cells as needed.

Chloride is taken into the body through food and table salt, which is made up of sodium and chloride molecules. Most of the chloride is absorbed by the gastrointestinal tract, and the excess is excreted in urine. The normal blood level remains steady, with a slight drop after meals (because the stomach produces acid after eating, using chloride from blood).

Is any test preparation needed to ensure the quality of the sample?

Blood chloride testing is often ordered, along with other electrolytes, as part of a regular physical to screen for a variety of conditions. These tests may also be ordered to help diagnose the cause of signs and symptoms such as prolonged vomiting, diarrhea, weakness, and respiratory distress. If an electrolyte imbalance is detected, the doctor will look for and address the disease, condition, or medication causing the imbalance and may order electrolyte testing at regular intervals to monitor the effectiveness of treatment. If an acid-base imbalance is suspected, the doctor may also order blood gas tests to further evaluate the severity and cause of the imbalance.

In persons with too much base, urine chloride measurements can tell the doctor whether the cause is loss of salt (in cases of dehydration, vomiting, or use of diuretics, where urine chloride would be very low) or an excess of certain hormones such as cortisol or aldosterone (where urine chloride would be high). Urine tests for chloride are also used, along with sodium, to monitor persons put on a low-salt diet. If sodium and chloride levels are high, the doctor knows that the patient is not following the diet.

Some of these tests may be ordered at regular intervals when a patient has a disease or condition or is taking a medication that can cause an electrolyte imbalance. Electrolyte panels or basic metabolic panels are commonly used to monitor treatment of certain problems, including high blood pressure (hypertension), heart failure, and liver and kidney disease.

A urine chloride test may be performed along with a blood or urine sodium when evaluating the cause of low or high blood chloride levels. The doctor will look at whether the chloride measurement changes mirror those of the sodium. This helps the doctor determine if there is also an acid-base imbalance and helps to guide treatment.

Increased levels of blood chloride (called hyperchloremia) usually indicate dehydration, but can also occur with other problems that cause high blood sodium, such as Cushing's syndrome or kidney disease. Hyperchloremia also occurs when too much base is lost from the body (producing metabolic acidosis) or when a person hyperventilates (causing respiratory alkalosis).

Decreased levels of blood chloride (called hypochloremia) occur with any disorder that causes low blood sodium. Hypochloremia also occurs with prolonged vomiting or gastric suction, emphysema or other chroniclung diseases (causing respiratory acidosis), and with loss of acid from the body (called metabolic alkalosis).

Drugs that affect sodium blood levels will also cause changes in chloride. In addition, swallowing large amounts of baking soda or substantially more than the recommended dosage of antacids can also cause low chloride.

(1995-2004). Minerals and Electrolytes. The Merck Manual of Medical Information – Second Home Edition [On-line information]. Available online at http://www.merck.com/mmhe/sec12/ch155/ch155a.html?qt=electrolytes&alt=sh through http://www.merck.com.